Method of operating a pumping system

Abstract

A pumping system has a motor ( 32 ) for driving a pumping mechanism ( 30 ). A variable frequency drive unit ( 36 ) has an input for receiving electrical energy of relatively high power and first, fixed frequency from a power supply, and an output coupled to an input ( 46 ) of the motor for supplying electrical energy of relatively low power and second, variable frequency to the motor. This second frequency preferably has a maximum value greater than the first frequency. A control circuit ( 50 ) is provided for selectively coupling the motor input ( 46 ) directly to the power supply for the supply of the relatively high power energy to the motor to maximize the torque that can be produced by the pumping mechanism. After a period of time the control circuit terminates the direct coupling of the motor input to the power supply for the supply of the relatively low power energy to the motor.

I claim: 
     
       1. A method of operating a pumping system comprising a pumping mechanism, a motor for driving the pumping mechanism and a variable frequency drive unit having an input for receiving alternating current of relatively high power and first frequency from a power supply and an output coupled to an input of the motor for supplying alternating current of relatively low power and second, variable frequency to the motor, the second frequency having a maximum greater than the first frequency, the method comprising:
 supplying alternating current to the pump via the variable frequency drive unit; 
 reducing the frequency of the alternating current supplied by the variable frequency drive unit to produce a reduced frequency alternating current in response to an increase in a magnitude of the alternating current drawn by the motor from the variable frequency drive unit; 
 determining that the frequency of the reduced frequency alternating current is below the first frequency and in response, coupling the motor input directly to the power supply for the supply of said relatively high power alternating current to the motor. 
 
     
     
       2. The method according to  claim 1  wherein the pumping system comprises a set of movable contacts coupled to the power supply, movement of the contacts being selectively activated to directly couple the motor input to the power supply. 
     
     
       3. The method according to  claim 2  wherein the contacts are moved from an open to a closed position to directly couple the motor input to the power supply. 
     
     
       4. The method according to  claim 1  wherein the direct coupling is terminated according to a predetermined timing relationship. 
     
     
       5. The method according to  claim 1  wherein the direct coupling is terminated in dependence on an operational characteristic of the pumping system. 
     
     
       6. A method of operating a pumping system comprising a pumping mechanism, a motor for driving the pumping mechanism and a variable frequency drive unit having an input for receiving alternating current of relatively high power and first frequency from a power supply and an output coupled to an input of the motor for supplying alternating current of relatively low power and second, variable frequency to the motor, said second frequency having a maximum greater than the first frequency, the method comprising the steps of supplying said relatively low power alternating current from the drive unit to the motor, monitoring the second frequency, and when the monitoring indicates that the second frequency has reduced below, or a predetermined amount below, the first frequency, coupling the motor input directly to the power supply for the supply of said relatively high power alternating current to the motor. 
     
     
       7. The method according to  claim 6  wherein the direct coupling of the motor input to the power supply is subsequently terminated for the supply of said relatively low power alternating current from the drive unit to the motor in dependence on the magnitude of the alternating current drawn by the motor. 
     
     
       8. The method of  claim 1  wherein the direct coupling is terminated when the magnitude of the current drawn by the motor is determined to be below a sustainable value for the variable frequency drive unit.